1. Field of the Invention
This invention relates to a structure and a method for packaging a semiconductor chip such as an LSI chip or the like on a circuit substrate.
2. Description of the Related Art
As a method of packaging a semiconductor chip on a circuit board or substrate, one has been used which face down connects a semiconductor chip having a plurality of projected electrodes (bumps) formed on the surface thereof to an internal substrate having conduction patterns formed at their corresponding points of bumps.
Japanese Patent Application Laid-Open No. 5-41404 discloses this type of semiconductor chip packaging method. According to the method disclosed in the present publication, when respective bumps formed on a semiconductor device are joined to wiring patterns on a circuit substrate so as to fit the wiring patterns, a thermosetting resin sheet is bonded between the semiconductor device and the circuit substrate so that a state in which the respective bumps are pressed against their corresponding wiring patterns, is satisfactorily held.
However, the packaging method disclosed in the aforementioned publication has the potential that since the fixing of the semiconductor device to the circuit substrate at the time of completion of the packaging depends only on a bonding or joining power produced by the resin sheet, the bonding power will be reduced particularly when the area at which the resin sheet makes contact with each of the semiconductor device and the circuit substrate is small and contacts between the bumps and the circuit patterns will be at fault due to deterioration over time. Although the resin sheet and the circuit substrate have not referred to their thermal expansion coefficients in the aforementioned publication, stresses developed due to the difference in thermal expansion coefficient between the semiconductor device and the substrate when they are returned to the normal temperature after having been pressurized and heated, are concentrated on the bumps when the thermal expansion coefficients of the resin sheet and the circuit substrate are different from each other. Thus, there is a possibility that cracks may occur in the surface of the semiconductor device.